KneeEarly Radiographic Differentiation of Infantile Tibia Vara from Physiologic Bowing Using the Femoral-Tibial RatioMcCarthy, James J. M.D.*; Betz, Randal R. M.D.*; Kim, Andrew M.D.*; Davids, Jon R. M.D.†; Davidson, Richard S. M.D.*Author Information Study conducted at Shriners Hospitals for Children, Philadelphia, Pennsylvania, U.S.A. From the *Shriners Hospitals for Children, Philadelphia, Pennsylvania, and the †Shriners Hospitals for Children, Greenville, South Carolina, U.S.A. Address correspondence and reprint requests to Dr. James McCarthy, 3551 N. Broad St., Philadelphia, PA 19140, U.S.A. E-mail: email@example.com Journal of Pediatric Orthopaedics: July-August 2001 - Volume 21 - Issue 4 - p 545-548 Buy Abstract The authors hypothesized that the ratio of the femoral to tibial metaphyseal-diaphyseal angles (femoral-tibial ratio [FTR]) more accurately differentiates physiologic bowing from infantile tibial vara than the tibial metaphyseal-diaphyseal angle (TMDA). The purpose of this study was threefold: to determine the false-negative and false-positive error rate of the FTR and TMDA; to determine to the effect of rotation on the FTR and TMDA; and to determine the reliability of the FTR and TMDA measurements. An FTR < 1 resulted in a false-negative error rate of 10% and a false-positive error rate of 7%, whereas a TMDA > 13° resulted in a false-negative error rate of 23% and a false-positive error rate of 10%. The difference between internal and external rotation was not significant for the FTR, whereas it was for the TMDA. The FTR was found to have good interobserver and intraobserver reliability (0.78 and 0.98, respectively). © 2001 Lippincott Williams & Wilkins, Inc.